The present invention relates to optical fibers such as are used in fiber optic cables for communication purposes. The invention relates more particularly to a fiber optic assembly for holding two or more parallel optical fibers in desired positions with respect to one another to, for example, facilitate splicing or connectorization of the fibers.
Fiber optic cables have been developed containing two or more loose optical fibers within a buffer tube. The fibers within the buffer tube are free to move in various directions relative to each other, including longitudinally along the lengthwise directions of the fibers. Connection of the optical fibers of the cable to an optical device is accomplished with the aid of a connector designed to receive ends of the fibers. One type of connector is designed to have the fiber ends inserted into a rear end of the connector and pushed through channels defined in the connector until the end faces of the fibers protrude out an end face of the connector at a front end thereof. The fibers are then epoxied in place and cleaved at their ends protruding out from the connector end face, and finally the connector end face and fiber end faces are polished. With this type of connector, the ability of the optical fibers within the buffer tube to slide relative to each other assists, or at least does not hinder, the assembly of the connector on the ends of the fibers.
Another type of connector contains pre-polished optical fiber stubs having rear ends located internally within the connector for abutting with the ends of the cable fibers. The opposite front ends of the stubs are located proximate the front end face of the connector for mating with another-optical device. The connector is attached to the cable fiber ends by inserting the fiber ends into the rear end of the connector and sliding the fibers forward until their ends abut the rear ends of the stubs, and then the fibers are clamped into place by operating a cam member of the connector. In practice, before the fiber ends are inserted into the connector they are first prepared by laying them side-side on a mechanical cleaver and cleaving them to precisely the same length. After cleaving, however, it is possible for the fibers in the buffer tube to slide relative to each other, such as when handling the fibers and inserting the fibers into the connector. This movement between the fibers makes it difficult to place each fiber into proper abutting contact with the corresponding stub of the connector.
The present invention seeks to overcome the problems noted above by providing an optical fiber assembly in which two or more optical fibers are tacked to each other to prevent relative sliding therebetween, while allowing the fibers to be easily detached when desired. In accordance with a first aspect of the invention, the optical fiber assembly comprises a plurality of optical fibers arranged parallel to one another such that each optical fiber is closely adjacent to at least one other optical fiber, and a web of material disposed between each pair of adjacent optical fibers and bound to said fibers at opposing surfaces thereof, the web lightly tacking the adjacent fibers together to prevent relative sliding between the fibers along a longitudinal direction thereof and being readily broken when pulling forces are exerted on the fibers away from each other transverse to the longitudinal direction such that the fibers can be separated without the fibers being broken by the pulling forces. Preferably, after the fibers are tacked together they are enveloped in a buffer tube that serves to protect the fibers. The assembly can then be incorporated into a fiber optic cable.
The web binding the fibers together can be provided in various ways. In one embodiment of the invention, the optical fiber assembly is formed by placing a plurality of optical fibers side-by-side and parallel to one another such that adjacent fibers are closely spaced apart, applying a hardenable composition in a fluid state onto the fibers such that the composition fills a space between each pair of adjacent fibers, removing the composition from surfaces of the fibers other than opposing surfaces of adjacent fibers such that all surfaces of the fibers except for said opposing surfaces are substantially free of the composition, and causing the composition to harden, whereby webs of the hardened composition are attached between said opposing surfaces of adjacent fibers so as to bind the fibers together.
The fluid composition can be of various types, including but not limited to heat-curable and radiation-curable (e.g., UV-curable) compositions, and can be applied to the fibers by passing the fibers through a bath of the composition. The side-by-side fibers can then be passed through an aperture of a tool such that edges of the aperture scrape the composition off the surfaces of the fibers except for the opposing surfaces between which it is desired to form a web. The remaining composition between the fibers can then be hardened, such as by heating in the case of a heat-curable composition, or by exposing the composition to radiant energy in the case of a radiation-curable composition.
In accordance with another embodiment of the invention, the optical fiber assembly is made by coating each of a plurality of optical fibers with a hardenable composition in fluid form, placing the coated optical fibers side-by-side and parallel to one another, pressing adjacent fibers against each other while the composition is still fluid such that the coatings on the fibers meld together to form a web of the composition between the fibers, and causing the composition to harden such that adjacent fibers are bound together by the web of the composition. In this embodiment, the hardenable composition can comprise a coloring composition that is applied to impart a particular color to the fibers for identification purposes. Thus, the coloring composition can serve both coloring and binding purposes. The composition can be of various types, including but not limited to a solvent-based composition that hardens upon evaporation of the solvent, a heat-curable composition, or a radiation-curable composition.
In yet another embodiment of the invention, the fibers are provided to have a solid coating of a composition that is soluble in a solvent. For example, the coating can be a soluble ink for coloring the fibers. A quantity of the solvent for the coating composition is applied to at least a portion of the solid coating of each of the fibers so as to cause the composition to become softened and tacky. The fibers are then pressed together such that the tacky parts of the coatings of adjacent fibers meld together, and the solvent is allowed or caused to evaporate so that the composition becomes solid again, thus binding the fibers together.
The fiber optic assembly in accordance with the invention can have the web between fibers formed as a plurality of discrete web sections that are spaced apart in the lengthwise direction of the fibers, i.e., an intermittent web. The web, whether continuous or intermittent, is strong enough to prevent sliding of one fiber relative to the other, but is weak enough to allow the fibers to be pulled apart with relatively little force such that the optical fibers are not broken. Once pulled apart, the fibers are substantially free of any binding material that would have to be removed prior to cleaving and inserting the fibers into a connector. Thus, the optical fiber assembly of the invention is different from a conventional optical fiber ribbon in which the fibers are totally enveloped in a matrix of material having a relatively high modulus and hardness, such that the matrix material must be peeled off the fibers before the fibers can be separated from one another.